In the drilling, downhole completion, production, transport, storage, and processing of crude oil and natural gas, including waste water associated with crude oil and gas production, and in the storage of residual fuel oil, H2S and/or mercaptans are often encountered. The presence of sulfur-containing species such as H2S and mercaptans is objectionable because they often react with other hydrocarbons or fuel system components. Another reason that the H2S and mercaptans are objectionable is that they are often highly corrosive. Still another reason that H2S and mercaptans are undesirable is that they have highly noxious odors. The odors resulting from H2S and mercaptans are detectable by the human nose at comparatively low concentrations and are well known. For example, mercaptans are used to odorize natural gas and used as a repellant by skunks and other animals.
The predominant H2S and mercaptan scavengers for natural gas and crude oil are water soluble monoethanolamine (MEA) triazines and monomethylamine (MMA) triazines. These compounds contain nitrogen and when used in sufficient concentration may cause problems for certain refineries. Glyoxal (C2H2O2) or acrolein (C3H4O) have been used as H2S scavengers in instances where a nitrogen-containing H2S scavenger is not desired. Glyoxal is a slow acting scavenger and may be corrosive to mild steel. Acrolein is an effective scavenger but an extremely toxic substance which operators do not like to use.
Oil soluble amine formaldehyde reaction products such as the dibutylamine/formaldehyde reaction product have been used previously as hydrogen sulfide scavengers. The generic structure of oil soluble amines is given below:
wherein R1, R2, R3 and R4 may be independently a saturated or unsaturated hydrocarbon group, e.g., alkyl, aryl, alkylaryl, alkaryl, cycloalkyl, alkenyl, aralkenyl, alkenylaryl, cycloalkenyl, and the like or heterocyclyl groups and R5 may be hydrogen or lower alkyl.
It would be desirable if a new class of H2S and mercaptan scavengers could be discovered which is very effective, but which is more efficient and increases the reaction rate as compared with prior scavengers.